need help choosing best ztr. have 6 acres to mow. i have looked at gravely, grasshopper and scag ,all are close in price ,but i have no experience with any of the engine options ie-diesel vs gas (air or liquid cooled),kohler,kawasaki,kubota, etc. also not sure which are best in terms of ease to service and maintenance. also is there any difference in longevity between mid mount and out front mowers. thank-you for any advice.